Electronic devices, such as mobile phones, can include external connectors for interfacing with peripherals. For example, one external connector can be an audio jack, e.g., an audio socket. The audio jack can be coupled to an audio plug of a pair of headphones, a microphone headset, or other peripheral device. The peripheral device can be coupled with the electronic device using an audio jack plug.
An electronic device can determine whether the peripheral device is plugged in based on comparing the voltage at a terminal of the external connector to a predetermined voltage. The predetermined voltage can be specified by the electronic device. Generally, a compatible peripheral device has a load, e.g., a resistor, that causes the voltage at the terminal to drop below the predetermined voltage when the peripheral device is connected to the terminal. That is, compatible peripherals can be manufactured according to voltage drop requirements of the electronic device. When the electronic device detects that the voltage has fallen below the predetermined voltage, e.g., using voltage detection circuitry, the electronic device determines that the peripheral is plugged in. On the other hand, when the electronic device does not detect that the voltage has fallen below the predetermined voltage, the electronic device determines that nothing is plugged in.